Method and device for producing a tomosynthetic 3D x-ray image

Abstract

In a method and device for producing a tomosynthetic 3D x-ray image, a number of 2D projection images of an examination subject are acquired using a fixed x-ray source. The x-ray source has multiple, individually controllable emitters that respectively emit a single x-ray dose from various different directions. The tomosynthetic 3D image is reconstructed from the individual 2D projection images, and at least one 2D projection image is composed of multiple individual images.

Description

BACKGROUND OF THE INVENTION[0001]1. Field of the Invention[0002]The invention concerns a method that is in particular suitable for mammography, as well as a device to generate a tomosynthetic 3D x-ray image. In such a tomosynthetic method, a number of x-ray images of an examination subject are acquired from different directions. The tomosynthetic 3D x-ray image is subsequently calculated from the 2D projection images obtained in this way.[0003]2. Description of the Prior Art[0004]A tomosynthetic 3D x-ray image is an image data set that is composed of slice images. Such an image data set acquired via reconstruction of 2D projection images is designated in the following as a tomosynthetic 3D x-ray image or 3D tomosynthesis image.[0005]Mammography concerns an x-ray examination of the breast with the goal of detecting malignant tumors at an optimally early stage. Through continuous improvement of imaging methods it is sought to generate x-ray images with greater significance in order to...

AI Technical Summary

Benefits of technology

[0010]An object of the present invention to provide a method and a device to generate a tomosynthetic 3D x-ray image which allow an exposure of an examination subject with a higher dose.

[0012]The method according to the invention has the following advantages. Since the maximum individual dose that can be generated by a single emitter of the x-ray source is limited, a plurality of single images can be generated via repeated activation of the same emitter, and thus the dose provided for the exposure of a 2D projection image can be increased. Moreover, by repeated activation of individual emitters the possibility arises to adjust a distribution of the total dose emitted by the x-ray source. For example, a few projections of the examination subject can thus be acquired with a higher dose, which leads to the situation that the quality of the subsequently computed tomosynthetic 3D x-ray image can be improved. By the individual activation of the emitters it is moreover possible to compensate for a non-uniform dose distribution in the 3D tomosynthesis image that is due to the exposure geometry. This is explained using the following example. An examination subject is often a female breast fixed between two compression plates. Those x-rays which emanate from the emitters that enclose a small angle with a surface normal of the aforementioned compression plates travel a comparably short path through the examination subject. In contrast to this, those x-rays which emanate from emitters that enclose a large angle with the surface normals travel a comparably longer path through the examination subject. The individual dose emitted by such emitters is therefore severely attenuated. The consequence is a non-uniform dose distribution that can be compensated in that those emitters that enclose a large angle with the surface normal emit multiple individual doses to generate a 2D projection image.

[0014]In an x-ray source having multiple emitters that can be activated individually, the x-ray dose that can be released by a single emitter is limited, since the danger exists that the (comparably small) x-ray emitter thermally may overheat. To solve this problem, after a first emitter has been activated to emit a first individual dose, an additional emitter different from the first emitter is activated first before this first emitter is activated again to emit an additional individual dose. At least the emission time of the additional emitter is thus provided as a cooldown time. It is possible for a longer cool-down time to occur for the first emitter. For this purpose as many additional emitters as possible can be activated between the individual emission processes of a specific emitter, the individual doses of which additional emitters are likewise used to generate the 3D tomosynthesis image. A maximum cooldown time is thus provided for the first activated emitter without the exposure time for the entire tomosynthetic 3D x-ray image being extended.

[0018]For further simplification of the activation, according to a further embodiment a constant product of current and emission time is provided for all emitters of the x-ray source. It is thus advantageously possible to control the exposure of a 2D projection image merely via the number of required individual doses.

[0019]The object is moreover achieved with a device according to the invention wherein the x-ray source of the device has at least one emitter that has a field emission cathode which is formed of carbon nanotubes. Moreover, the device has an x-ray detector with low inherent noise. With a field emission cathode whose field emitter consists of carbon nanotubes, it is possible to generate individual x-ray doses with nearly arbitrary temporal shape. Moreover, such cathodes can easily be miniaturized. An x-ray detector with low inherent noise is particularly advantageous since multiple individual images are added to calculate a 2D projection image. A low inherent noise of the x-ray detector prevents that a 2D projection image with a poor signal-to-noise ratio is obtained as a result of the addition of the individual images.

Problems solved by technology

The individual dose emitted by such emitters is therefore severely attenuated.

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